ISIS Adjacencies filtration

Configure all router running ISIS protocol

R1# interface Loopback0  ip address 1.1.1.1 255.255.255.0  ip router isis 1 ! interface FastEthernet0/0  ip address 10.1.12.1 255.255.255.0  ip router isis 1 ! router isis 1  net 49.0001.0000.0000.1111.00

R2# interface Loopback0  ip address 2.2.2.2 255.255.255.0 ! interface FastEthernet0/0  ip address 10.1.12.2 255.255.255.0  ip router isis 1 ! interface FastEthernet0/1  ip address 10.1.23.2 255.255.255.0  ip router isis 1 ! router isis 1  net 49.0023.0000.0000.2222.00

R3# interface Loopback0  ip address 3.3.3.3 255.255.255.0  ip router isis 1 ! interface FastEthernet0/0  ip address 10.1.23.3 255.255.255.0  ip router isis 1 ! router isis 1  net 49.0023.0000.0000.3333.00

Let's check neigbhor in R2:

R2#show isis ne

System Id      Type Interface   IP Address      State Holdtime Circuit Id

R1             L2   Fa0/0       10.1.12.1       UP    27       R2.01             

R3             L1   Fa0/1       10.1.23.3       UP    8        R3.01             

R3             L2   Fa0/1       10.1.23.3       UP    7        R3.01   

We can see R2 establish neighbor to R1 and R3.

Let’s config on R2, which remove neighbor to R3.

R2#

 clns filter-set AF deny 49.0023.0000.0000.3333.00          //deny only this NET address

 clns filter-set AF permit default                                            // allows any other neighbor

!

interface FastEthernet0/1

 ip address 10.1.23.2 255.255.255.0

 ip router isis 1

 isis adjacency-filter AF

Verify:

R2#show isis ne

System Id      Type Interface   IP Address      State Holdtime Circuit Id

R1             L2   Fa0/0       10.1.12.1       UP    27       R2.01             

It only establish neighbor with R1.

See debug:

R2#debug isis adj-packets

IS-IS Adjacency related packets debugging is on

*Mar  1 00:21:14.751: ISIS-Adj: Rec L2 IIH from c200.0704.0000 (FastEthernet0/0), cir type L1L2, cir id 0000.0000.2222.01, length 1497

*Mar  1 00:21:15.299: ISIS-Adj: Sending L2 LAN IIH on FastEthernet0/0, length 1497

*Mar  1 00:21:15.391: ISIS-Adj: Rec L2 IIH from c203.0bc8.0000 (FastEthernet0/1), cir type L1L2, cir id 0000.0000.3333.01, length 1497

*Mar  1 00:21:15.395: ISIS-Adj: Adjacency disallowed by filter

*Mar  1 00:21:16.775: ISIS-Adj: Rec L1 IIH from c200.0704.0000 (FastEthernet0/0), cir type L1L2, cir id 0000.0000.1111.01, length 1497

*Mar  1 00:21:16.779: ISIS-Adj: Area mismatch, level 1 IIH on FastEthernet0/0

*Mar  1 00:21:16.959: ISIS-Adj: Rec L1 IIH from c203.0bc8.0000 (FastEthernet0/1), cir type L1L2, cir id 0000.0000.3333.01, length 1497

*Mar  1 00:21:16.963: ISIS-Adj: Adjacency disallowed by filter